One of the major advances in communications in recent years has been the increased use of optical fiber systems for carrying large quantities of information with low distortion and low cost over great distances.
Optical delay lines are important components in such optical fiber communication systems. They are critical components in switching streams of optical signals from one path to another. They are used in packet switching for Internet applications, and they are building blocks in the correlation filters used to recognize packet addresses for the Internet. Delay lines are also used in the buffers that control the timing of signal routing. And they are used for synchronizing data bits, for compensating dispersion between different optical paths, and for compensating differential delay between paths.
Variable delay lines are needed because different delays may be required at different times. In addition to variation required by the dynamics of optical network components, variation of delays in the optical network may be required to compensate differences in RF transmission paths due, for example, to changes in a satellite orbit, to spaced apart multiple ground antennas, or to atmospheric scintillation.
Conventional variable optical delay lines are incremental rather than continuously variable. A typical conventional variable delay line comprises a plurality of optical fibers, each cut to a slightly different length, and an optical switch to select the fiber path, thereby selecting the delay time. Since the differences in length are incremental, the delay line is incremental rather than continuous. Thus the variable delay line can only approximate the precise delay being sought.
Accordingly it would be advantageous to provide an improved variable optical delay line that provides continuous resolution over a large dynamic range.